President Trump's legal team is growing by one. The move comes as Trump, more directly, goes after special counsel Robert Mueller and his investigation. White House press secretary Sarah Sanders says the president is simply expressing his frustration through tweets - even as the White House and Trump's outside lawyers say they are cooperating fully with the probe. NPR White House correspondent Tamara Keith has this look at what Trump's legal team has been saying.

TAMARA KEITH, BYLINE: The newest member of President Trump's outside legal team, Joe DiGenova, is a former federal prosecutor and well-known Washington lawyer. But it's more likely that his appearances on Fox News criticizing the Russia investigation are what landed him the gig. This was DiGenova on Fox in January.

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JOE DIGENOVA: There was a brazen plot to illegally exonerate Hillary Clinton and - if she didn't win the election - to then frame Donald Trump with a falsely-created crime.

KEITH: And here he was again on Fox just the day before Attorney General Jeff Sessions fired former acting director of the FBI Andrew McCabe.

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DIGENOVA: This system of equal justice has been rent asunder by the conduct of James Comey, America's best-known dirty cop, Andrew McCabe and others, including senior Obama administration Justice Department officials.

KEITH: Another member of Trump's outside legal team, Jay Sekulow, hosts a national call-in show where he too weighs in on developments in the investigation.

KEITH: On this edition of the show, Sekulow didn't offer much of his own analysis. But last month when Mueller's team secured the indictments of 13 Russians and three Russian entities for using social media and even organizing rallies to interfere in the U.S. election, Sekulow used his show to downplay the development.

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SEKULOW: Also, it was a program that started in 2014 - well before the election. So this was part of a - looks like an ongoing move by the Russians to engage this kind of issue is what it seems like to me. And then again, it predates the presidential campaign of Donald Trump.

KEITH: Another outside lawyer John Dowd said, over the weekend, he thinks the investigation should be shut down but also described ongoing discussions with the office of special counsel as productive and constructive. That's more in line with the approach taken by the lawyer inside the White House handling the Mueller investigation, Ty Cobb, who has emphasized cooperation and insists the president has no intention of firing Mueller. So what exactly is the strategy?

STEPHEN SALTZBURG: I think there's a little bit of good cop, bad cop going on here.

KEITH: Stephen Saltzburg is a professor at George Washington University Law School. Cobb is the good cop, and the outside lawyers are doing more of the bad-cop routine, Saltzburg says.

SALTZBURG: And I think Joe DiGenova's addition is part of the bad cop.

KEITH: But Saltzburg, who was on the independent counsel team investigating Iran-Contra and has known Mueller for a long time, says this approach must be more about undermining the investigation in the court of public opinion than actually changing how Mueller conducts his probe.

SALTZBURG: He's a very disciplined prosecutor. I don't think this is going to exacerbate his approach. In other words, it's not going to make him tougher on the president, but it's not going to soften him up either.

KEITH: One other audience for all these tough public statements - their own client, President Trump. Tamara Keith, NPR News, the White House.